Let me try to explain this movie continuity thing
Both the Avengers and Deadpool are technically Marvel movies but Deadpool isn’t part of the MCU (Marvel cinematic universe.)
Marvel went bankrupt in the 90s and had to sell off different franchises so although in the comic books they still have control over everything they now don’t own the rights to a lot of the characters in movies and TV.
MCU is technically owned by Disney and they own the Avengers franchise.
The X-Men franchise is owned by Fox.
It’s been getting complicated because what people own isn’t exactly so straightforward… Wolverine has been an Avenger but he’s also a mutant and part of the X-Men and since he’s more well known for being part of the X-Men Fox got to keep him. Quicksilver and Scarlet Witch are mutants and did start out in the X-Men comics but for the most part they’ve always existed in the Avengers so Disney got them…but Fox still wanted them and after some fighting was allowed to have Quicksilver but they had to give him a new name.
Then you have Spiderman. The Spiderman franchise is owned by Sony but he is also an Avenger. After some arguing Sony and Disney decided to work together so that’s why we now have Spiderman in the Avengers but he’s a different Spiderman than the ones we saw in the last movies.
The Spiderman that Andrew Garfield plays is owned solely by Sony and lives on Earth 120703 where as the new one lives with Captain America and Iron Man on Earth 199999. All of the X-Men and Deadpool live on Earth 10005.
All of the characters you see in the regular comic books live on Earth 616.
Now I’ll make this a little more confusing and a lot more useful to you guys.
Disney isn’t allowed to use Deadpool but he would technically still exist in their universe and it’s completely up to the fans to decide what they think he is in that universe. He could still be Deadpool but we just never see anyone mention him but he could also just be Wade Wilson. Maybe he never even got cancer. Maybe he still in high school with that universe’s Spiderman. That could completely justify your high school AUs.
Fox isn’t allowed to use Spiderman but again he would technically exist in that universe. On Earth 10005 which is where we see Deadpool in his movie Peter Parker could be anything. He could have been born a woman or have gone on to become that universe’s Captain America while Steve Rogers became Spiderman. We will never know because Fox is not allowed to tell us so whatever you decide isn’t necessarily not true.
Every time you see characters show up someplace new they do exist within Marvel continuity, they just come from different universes. 10005 Deadpool (from the movie) is technically a different guy from 616 Deadpool (from the comics) so technically they could travel to each other’s universes and team up.
